1. Field
Aspects of the invention relate to a method and a device for measuring a current flowing in an electrical conductor.
2. Discussion of Related Art
In the automotive field, the increasing number of power consuming devices is placing a constantly growing energy demand on the vehicle electrical system. In particular, this increased energy demand places increasing loads on a vehicle's battery, which serves as a buffer during the operation of the vehicle's engine and maintains the vehicle's power supply when the engine is off. When the vehicle is frequently used for short-distance trips, the result may be that the battery is not fully charged while the engine is on. This can result in the vehicle being left with a discharged battery or being difficult if not impossible to start because the battery voltage is too low. This situation may be compounded in motor vehicles that place such a high energy demand on the vehicle's electrical system.
To reduce these and other effects, energy management systems are increasingly being used in vehicles. An energy management system typically is used to ensure that the battery's charge state does not enter a critical condition and maintain a positive battery charge balance. Such a system analyzes the battery condition based on measured variables such as ‘battery current’, ‘battery voltage’ and ‘battery temperature’. Particular importance is placed on the determination of the battery charge current or discharge current in order to keep the battery at a non-critical charge level and to ensure that the vehicle is able to start.
To determine the charge current or discharge current, the system must measure currents over a very wide range, for example from −200 A to 1500 A. Therefore, a suitable sensor for the energy management system in vehicles has to cover this wide range, that is, it must have a high dynamic response.
A prior art sensor system for use in a motor vehicle for monitoring the flowing currents is shown schematically in FIGS. 9 and 10. To determine the battery current, a measuring resistor 202 is inserted in the ground lead 201. Suitable evaluation electronics 203 directly measure the voltage drop at the measuring resistor and calculate the flowing current. The measuring resistor can, for example, be made of manganin.
FIG. 9 is a schematic representation of the measuring arrangement utilizing this sensor. An automotive battery 205 is connected by a ground lead 201 to the vehicle ground. The sensor, comprising the measuring resistor 202 and the evaluation electronics 203, is integrated in the ground lead 201. Electrical power consuming devices 206 in the motor vehicle are connected to the positive pole of the battery 205 via a line 207.
One drawback of this prior art arrangement stems from the fact that the measuring resistor has to be integrated in the current-carrying conductor. This arrangement involves additional design costs because it is necessary to ensure that shear and tensile forces are kept away from the measuring resistor. Deformation of the measuring resistor can influence the result of the measurement and, in extreme cases, results in a defective sensor. A further drawback is the fact that power loss dissipation necessarily occurs across the measuring resistor. Even when small resistors are used, for example a 100 μΩ measuring resistor, heat is still is generated and must be dissipated.